Method of effecting soaring flights and aeroplane therefor



1 Nov. 26, 1929. A, HA sTE-D v 1,737,191

METHOD OF, EFFECTING S'QARING 1 11111111 5 AND AEROPLANE' THEREFOR Original Filed May 2 1921 s Sheets-Sheet 2 5 1929- 7 A., HALSTED' 33 'METHUD QF EFFECTING SOARING FLIGHTS AND AEROPLANE THEREFOR Original Filed May 26. 1931 -3 Sheets-Sheet 5 WIND Fonwnrm AIR v uocnv Patented Nov. 26,; 1929 UNITED STATES- PATENT OFFICE r ARTHUR HALSTED, OF CLARENDON, VIRGINIA ivinrn-oi) or? nrrnorine soAnme rmen'rsnnn AnnornANn rnnnnron Application filed May 26,1921, Serial H0. 472,783. Renewed April .18, 1929.

My invention relates to aeronautics and particularly to soaring flight as distinguished from an engine propelled or gliding flight.

In all known aeroplanes the power news sary for supporting the aeroplane and for propelling it through the air is supplied by an engine carried by the aeroplane. With these known constructions it is impossible/tor e moving air currents or wind. I

My invention will be best understood by a brief consideration of some of the conditions relating tosoaring flight, I At certain elevations above the earth the air current or wind represents a practically inexhaustible supply of energy. Between the elevations of 1500 and'3000 feet the air currents are substantially horizontal, of rela tively highvelocity to 80 miles per hour) 30 and are not subject to rapid changes in velocity or direction. Some prior attempts to. solve the problem of withdrawing energy from the wind by a body supported in and by the wind have been based upon the theory .-that rapid pulsations were continuously taking place in the air currents, but recentobservations have shown that these rapid pulses tions do not occur at the elevations stated.

Sailboats; windmills and similar devices are able to absorb kinetic energy in a continuous. manner since they remain substantially stationary with respect to the earth and consequently do not take up a drift 'withthe wind. When an object is supported in the wind'but not connected to the earth, it will absorb energy until entrained in the wind i. e. drifting with the Wind. Once the object is entrained in the wind no further increase in kinetic energy is possible until its drift velocity is reduced so that the wind may again act upon the object.

It is therefore apparent that a soaring aeroplane must be capable of moving out of entrainment with the wind as soon as the wind ceasestosupply kinetic energy to the aeroplane. In other words the aeroplane must continuously. repeat the cycle which comprises'thestep of absorbing kinetic energy, which step results in entraining the aeroplane in the wind, and the step of moving into position to absorb kinetic energy, i. e.

detraining from the wind.

The addition of a sail area toian aeroplane enables the aeroplane to absorb energy from r the wind inaneflicient manner.- In View of the conditions above stated however it is evident that the mere addition of a sail area does not solve the roblem of soaring flight. The sail area must he so arranged and so manipulated that the detraining from the wind is accomplished by the expenditure of little or no energy. While it might seem impossible that the drift velocity of the aeroplane could be brought to zero without loss of en ergy, this result may be secured by transforming the kinetic energy due tothe drift velocity into potential, energy... The drift velocity of the aeroplane may be turned upwardly by the proper manipulation of a sail area to provide an upward force and when the drift velocity is so altered the kinetic energy due to the drift velocity will move the mass of the aeroplane upwardly against the force of gravitv. Under proper conditions and excepting triction losses',.when the drift velocity is reduced to ero the entire kinetic energy due to drift v locityrwill have been transformed into potential energy. Exceptmg the work incidental to the manipulation of the sail area no work will be done in thus stopping the drift velocity when the applied force is a centripetal force. When the drift velocity becomes zero the aeroplane ma again absorb kinetic energy from the win My invention contemplates the provision of an aeroplane designed in accordance with the principles above outlined.

An object of my invention is to provide an aeroplane capable of maintaining soaring ,vention are illustrated in flight and a further object of my invention is to provide an aeroplane with a sail area for absorbing kinetic energy from: the wind, and more specifically an object'of my invention is toprovide an aeroplane with a sail area eflectivein a plane or planes paraL lelto the plane of symmetry of the aeroplane, and which sail area is of reversible camber and is capable of movement longitudinally of the aeroplane. 1

According to the method under which my aeroplane operates, energy for propelling and supporting the aeroplane is supplied to the aeroplane in a substantiallycontinuous manner. More particularly, the method under which my aeroplane operates comprises the withdrawal of kinetic energ from the wind during the entrainment o the aeroplane in the wind and the transforming of a part of the kinetic energy thus obtained into potential energy to support the aeroplane during the detrainfnent from the wind.

Specific embodiments of aeroplanes which will attain these and other objects of my inthe accompanying drawings in which Fig. 1 is a side elevation of an aeroplane embodying my invention;

Figs. 2 and 3 are respectively, a'plan and a front elevation of the same;

Fig. 4 is a side elevation ofan airfoil mounting; v

Fig. 5 is an end elevation of the same;

. Fig. 6 is a. section on line 6-6 of Fig. 4;

Fig. 7 is a vector diagram of the forces set up at one period-of the. soaring flight, and

One specific embodiment of my invention as applied to a monoplane is illustrated in Figs. 1 to 3 inclusive. The monoplane may be of any desired type and as here shown includes a supporting plane or wings 1, 1 horizontal stabilizer and elevator 2 and rudder 3. The aeroplane is provided with a sail area 1 for taking up kinetic energy from the wind, and as shown, the sail area comprises a plurality of airfoils which are camberedto any desired airfoil section. Airfoils 1, 4 are mounted on suitable supports above the wings 1, 1 and airfoils 5, 5 are mounted below the wings 1, 1', the areas and relative location of the airfoils being such that the resultant of the wind pressures upon the airfoils will pass approximately through the center of gravity of the aeroplane. The ratio of sailarea to supporting areamay be varied within a wide range but I findthat the best-results are obtained when the sails have an area equal to twenty to twenty-five per cent of the area of the supporting wings. As shown in Figs. 1

and 3 the said airfoils are parallel to the sup-.

porting wings 1, 1, and this is the normal position of the airfoils during gliding or power' flight, during which flights they act as supplemental supporting surfaces. Each of said 90. As shown in dotted line in postsor shafts 10 upon which an airfoil is mounted for oscillatory movement. The details of theairfoil construction are not shown as the specific design of the airfoils does not form part of my invention; A specific means of mounting an airfoil is shownin Fig. 6,

the airfoil comprising in reality twov airfoil sections 11, 11' which are pivotall mounted on the shafts 10 as by cylindrical aring 12 which are arranged in the airfoil sections parallel to the entering edge and near the mean position of the center; of pressure of the airfoil. Adjacentthe sleeve 9 the trailing edge of the airfoil sections 11, 11' are connected to arcuate racks 13, 13, and said racks may be operated from a motor '14, through gearin 15 which is preferably of the nonreversi le type. Motor 14. and gearing 15 are carried by sleeve 9 and flexible leads'16 connect the motor to a source of current, for

' example a storage battery. By the use of any suitable system of electric control, the details of which form no part of this invention, all of the motors 14 are made to operate in unison. Oscillation of the airfoils about shafts 10 varies the angle of incidence Fig. 8 is a side elevation of a modification.

of the airfoils and a suitable control system .for motors 14; results in the same setting for each of the airfoil sections.

The axis 6 which carries the air foil may be rotated by means of an electric motor 17 through a worm 18 and gear 19 which is Keyed to axis6. Each motor is energized through circuit wires 20 and any suitable control is used so that all of the airfoils move in unison. By rotation-0f axes 6 the airfoils may be moved either clockwise or counterclockwise through any desired an le up to ig. 2 the individual a'ir foils have been rotated'through 90 in a clockwise direction as viewed from the front of the machine, and in addition the logs and consequently the airfoil positions .by

ybe

means of automatic controllers. Automatic controlsfor aeroplanes are well known in the art and any desired system of control may used. As the details of the control form no, part of my invention no description of such control is included herein.

As applied to a biplane my invention may take the form shown diagrammatically in.

Fig. 8, in which I and 1 indicate the two supporting planes and 4, 31%, 5 5, indicate two sets of airfoils supported between the planes and adapted to be maneuvered in the same manner as the airfoils above described. "As has been indicated above it is not necessary that the airfoils assumeposition normal to the supporting wings 1, 1. When normal to wings 1., 1 the maximum transverse and forward components of the lift force from the airfoils will be developed, but it is usually unnecessary and even undesirable to make use of the maximum forces which may be developed. When the airfoilsare set at an.

angl to wings 1, 1, the effective area of the airfoils'so far as forward and transverse lift forces are concerned is substantially equal to the projection of the airfoil areas upon the plane of symmetry of the aeroplane. An upward force is also developed which is substantially equal to that which would be de rived from an airfoil equal in area to the'projection' of the airfoils upon the wings 1, 1. The airfoils thus comprise in eflect a sail area effective in a plane or planes substantially normal to the supporting wings and this sail area is of reversible camber and iscapable of movement longitudinally of the aeroplane.

- It is not necessary that the sail area be capable of use as auxiliary supporting planes since it is possible to secure beneficial results by the use of a sail area or sail areas which at all times remain substantially normal to the supporting planes,but I find that it is advantageous to mount the airfoils so that they may function as supporting planes at certain times. The, means for supporting and maneuvering the airfoils may be varied at will so long as the sail area is capable of being maneuvered I (a) to present the concave side of the airfoils towards either side of the aeroplane, i. e. to reverse the camber,

b) to present the airfoils at any desired angle of incidence to the observed air stream, an

(0) to shift thecenter of pressure of the I airfoils longitudinally of the aeroplane.

The desired effects which are to be secured by these three adjustments of the sail area are, respectively,

(a) the application of a lift force having a transverse component directed toward either side of the aeroplane, I

(b) the securing of an eflicient angle'of attack of the sail area under conditions giving rise to a wide soaring an de,

('0) the application of a lift force having a component which does not pass through the center of gravity of the aeroplane, thus producing a turning moment as in'ruddering, for altering the soaring angle.

So far as I am now aware the most eflicient utilization of the energy of an air current can be secured with an apparatus which is capable of producing the three-effects above stated. j

By providing a sail area or sail areas capable of'securing the effects as statedit is possible to secure the soaring flight of an aeroplane along'paths of three distinct types. Assuming that the aeroplane is moving in an air current, soaring flight may take Place along any one of or along any desired combination of three paths, i..e.

(1) a tacking or zig-zag path,

(2) an orbital or a sinuous path substantially across the wind, or

(3) a. sinuous path substantially with or against the wind.

In the following discussion of the maneuvering of the aeroplane it is assumed thatthe aeroplane has been placed in the wind by any suitable means, as by an engine and propeller.

When suitably positioned in the .wind,*the

engine may be cutoff and energy maybe drawn from'the wind by the proper manipu-. lation of thesail areas. As may be readily determined mathematically the wind velocity necessary for soaring flight will depend upon the loading of the aeroplane and consequently upon its airvelocity, and usually will vary from fifty to one hundred percent of the air velocity of the aeroplane.

Whatever the path of flight to be followed the same methodof intermittent absorption of kinetic energy from the wind takes place. It is obviously impossible to absorb kinetic energy continuously since no energy can be absorbed from the wind when theaeroplane is entrained in the wind. By absorbing kinetic energy during entrainment in the wind and then utilizing a portion of that kinetic energy to move the aeroplane out of entrainment" with the Wind, and repeating this cycle it is possible to secure an intermittent but continuously repeated and substantially constant absorption of kinetic energy.

TAGKING PATH Entrainment in the wind Assuming the aeroplane with the airfoils acting as supporting planes to be flying across a wind but with no drift with the wind, there will be an air stream as observed from the aeroplane which isthe resultant of the velocity of the wind acrossthe aeroplane produce a rise in altitude.

and the air velocity due to the forward movement as observed on the "aeroplane. The angle between this'observed air-stream and the longitudinal axis of the aeroplane will be termed the soaring angle. The airfoils 4, 1, 5, 5 are now rotated about the axes 6 to bring them into position to absorb energy from the wind, and this movement may com prise rotation through into vertical position, or it' may comprise movement through a lesser angle. At the same time, and through the proper movement of motors 14 and racks 13 the airfoils are moved about shafts 10 to present a suitable angle of incidence to the observed air stream.

When the velocity of the wind is sufficient the forward component of the lift force will supply the flying losses and will also It is therefore possible to shut off the engine as soon as the maneuver above described is initiated.

The vector diagram of Fig. 7- represents the forces acting upon.the aeroplane when the airfoils are acting as fsail areas. For convenience, the entire sail area is illustrated as composed of a single airfoil 4% located substantially at the longitudinal axis of the aeroplane and this single airfoil is assumed to be normal to the supporting wings 1, 1,

though it will be understood that it is not the airfoils are not normal to wings 1,1 therewill be an upward component of the lift force which will tend to neutralize the force of gravity, but this component has not been considered in the vector diagram. In the vector diagram OL represents the lift force produced by the airfoil l the lift force acting normal to the observed air stream. The lift force OL may be resolved into a forward component OLZ and a transverse component ()Lt. The drag force which acts along the line of the air stream is represented by OD and is made up of the drag of the aeroplane Cd, and the drag of the sail area, (ZD. The drag OD may be resolved into its longitudie nal component ODZ andatransverse component ODt. The algebraic sum of the longitudinal components OLZ and ODZ indicatesthe force which is acting to propel the aeroplane, i. e. to supply useful energy to the aeroplane. The forward component'of'the lift force decreases as the aeroplane takes up a drift velocity since the soaring angle decreases as the drift increases.

'The transverse force acting to give the If desired the nose of the aeroplane may be turned away from the wind during the maneuver just described to increase the effective soaring angle and'this result may be attained by ruddering or by movingthe airfoils forwardly to produce aturning moment about the center 0 gravity.

- To enable the aeroplane to again'absorb energ from the wind the'aeroplane must be detralned from the wind.

' Detraebting.

7 When the aeroplane has taken up drift, the I soaring angle will become substantially zero and the air stream as observed fromthe aeroplane will be fore-and-aft. During the diminution of the soaring angle the airfoils will be rotated about shafts 10 to maintain the desired angle of incidence. When the soaring angle becomes substantially zero the airfoils are rotated about axes -6 into their ori :11 positions parallel to wings 1, 1. The lift orce during this movement of the airfoils has no longitudinal component as the soaring angle is practically zero, and the entire force is acting in a transverse direction. x This force acts in a line normal to the entering edge of the airfoil and consequently the force which at first acts with the drift of the aeroplane, swings into a vertical position acting ,up-

wardly when the, airfoils become parallel with wings 1, 1. As the force of gravity is balanced by the lift force of the. supporting wings the lift force from the airfoils produces an additional upward pressure on the aeroplane. This force acts as a centripetal force and alters the velocity of the aeroplane by turning it upwardly.

The turning movement of the airfoils is continued past parallelism with wings 1,1

anda lift force is set up which acts against the direction of the wind. As the soaring angle is negligible the lift 'force has no forward component but has an upward as well as a transverse component. This lift force acts in a plane substantially at right angles to the longitudinal axis of the aeroplane and consequently it acts in the plane of the drift velocity. The airfoils are so. maneuvered during this portion of the flight that the resultant of the lift force of the airfoils and the lift force of the supporting wings 1, 1

acts as a centripetal force. By thus causing the resultant of these forces to act perpendicularly to the drift velocity as it is. turned upwardly these forces have the same effect u on the aeroplane as the tension in a penduliim string has upon the pendulum. The flight path of the aeroplane, as projected upon a where R is the radius of the curvature of the flight path in feet, M is the mass of the aeroplane, V is. the drift velocity'in feet per sec 0nd and F is the centripetal force in pounds. As the applied force does no work upon the aeroplane the entire kinetic energy due to the drift velocity goes into potential energy or inused to support the aeroplane.

creased altitude. In soaring flight no power is applied to the aeroplane to supply flying losses during the detraining from the wind and therefore the curveof the flight path is modified by the flying losses. The time consumed in the detraining step is dependent upon the force used for detraining and if de sired the time maybe so chosen that the rise. inaltitude due to the increased potential flying losses forenergy will just balance the the detraining period.

During the time when the aeroplane is detrainingfrom the wind the sail area does not absorb energy from the windbut the nonuseful kinetic energy due to drift velocity is transformed into potential energy which is By this methodof maneuvering the sail area a substantially continuous supply of energy is available for maintaining the aeroplane in the air.

When the transverse velocity of the aeroplane is' substantially zero the airfoils are rotated back into and past parallelism with wings 1, 1 thereby assuming the position obtained by the maneuver first described in connection with this flight. This results in a transverse force tending to throw the nose' of the aeroplane away from the wind which will produce a soaring angle and this turning movement of the aeroplane may be assisted by ruddering or by a forward. positioning of the airfoils. The aeroplane is now in the posi tion which we assumed at the beginning of this description and the cycle of events above f jd'escribed may be repeated; the airfoils being first returned to position such that the lift forces pass through the center of gravity in case they had been shifted from that position for ruddering purposes. As the aeroplane detrains from the wind it is essential that no soaring angle appear. The-nose of the aeroplane therefore must be turned more and more into the windas the detraining progresses. This turning may result entirely from the action of the lift force of the sail, or the effect of the sail area may be modified by ruddering or by shifting the airfoils forwardly so that the combined lift forces there- \r from will act in advance of the center of gravity of the aeroplane. 4 I

Assume the airfoils to be parallel to wings 1, 1 and the aeroplane flying directly against the wind.

The airfoils are rotated about axis 6 towards a vertical position and moved about shafts 10 to give a desired angle of incidence to the air stream so as to produce a right or left-hand force as desired. The airfoils in this position will supply a centripetal force tending to giae the aeroplane an orbital flight path and to turn the aeroplane so as to produce a soaring angle between the observed air stream and the plane of symmetry of the. 6,5, aeroplane. As the soaringangle appears thew-1;" airfoils will be adjusted about shafts 10 to maintain a desired angle of incidence with the observed air stream.

By virtue of this soaring angle the airfoils are enabled to absorb kinetic energy from the wind during the time that the aeroplane changes direction from flying against the wind to flying with the wind, the action being substantially the same as described above in 0 connection with the tacking path of flight.

Detraim'ng The path tobe followed in he ading the aeroplane back into the wind may be a continuation of the first half of the turn, thus producing an orbital path or the curvature of the path may be reversed to give an S- path. For continuing the turn the airfoil settings remain unchanged while for reversing the turn the airfoils are rotated about axes 6 to secure a reversal of camber. The turn back to a position of flying against the wind is so made that the air stream will always be in the planeof symmetry of the aeroplane, thus producing no soaring angle. This result may be secured by varying the airfoil settings by rotation about axes 6 in such a manner as to give the aeroplane a skiding action or drift as observed from the earth. In other words the lift force or centripetal force acting on the aeroplane will be reduced until the turning has carried the aeroplane into a position of travel directly across the wind giving the aeroplane a full transverse ally produce a gain in elevation. In the secondhalf of the=turn the ground velocity falls 03 by twice the wind velocity.

The aeroplane is now in a position to repeat the maneuver.

As the longitudinal drift velocity is thus turned against the wind, the kinetic energy due to drift will tend to move the aeroplane forwardly at a speed in excess of its normal air speed, thus producing again in altitude which is available for supplying flying losses.

SINUoUs PATH or FLIGHT 'SUBs'rA 'rIALLY AGAINST OR WITH THE WIND For traveling substantially against or with the wind, the aeroplane utilizes the inertia of rotation about a vertical axis.

Entrainingin the wind Assume the aeroplane to be headed directly into the wind, and with the airfoils acting as supporting surfaces. The airfoils are rotated towards their vertical positions thus giving a transverse force tending to throw the nose of the aeroplane towards the side to which the convex camber of the airfoils is presented. 1 If desired, ruddering may be used to increase this turning of the aeroplane.

As the longitudinal axis of the aeroplane moves out of the direction of the wind stream, a soaring angle appears. As in the previous types of flight the airfoils are'rotated about shafts 10 to give the desired angleof incidence with the air stream. When a substantial soaring angle is attained the airfoils are moved rearwardly by means of the flexible wires or cords 23. The resultant of the lift forces of the airfoils now acts at a point in rear of the center of gravity of the aeroplane. The lift force has a forward component which supplies flying losses and when the wind velocity is adequate an increased elevation also results. The transverse component will tend to produce alateral velocity or drift and in addition gives the aeroplane an angular velocity of rotation about a vertical axis since it does not act at the center of gravity. This angular velocity of rotation tends first to decrease the soaring angle. As the soaring angle approaches zero the airfoils are rotated about axes 6 and reach their position parallel to wings 1, 1 when the soaring angle is substantially zero.

Detraz'm'ng At this time the airfoils are moved forwardly so that the resultant of all lift forces again passes through the center of gravity of the aeroplane. The rotation of the airfoils about axes 6 is continued and transverse and upward components appear at once while the forward component is still negligible. As in the process ofmaneuvering out of entrainment with the wind in the tacking flight, the kinetic energy due to drift is best utilized when the airfoils are so manipulated that the.

combined lift forces of the airfoils and the supporting wings acts as a centripetal force.

,The transverse component also assists the angular momentum in turning the longitudinal axis of the aeroplane to produce a soaring angle over the-other bow..- As an adequate soaring angle appears, a longitudinal component of the lift force furnishes flying losses as before, and the airfoils are again moved -rearwardly so thatthe transverse component may set up a turning movement reversing the previous angular movement of the aeroplane and tending to decrease the soaring angle.

The aeroplane is thereby moved back into position flying against the wind. The airfoils are moved back into position parallel with wingsl, 1, as the soaring angle approaches zero. The aeroplane is now in position to repeat the cycle above outlined.

In maneuvering as above described the most efiicient use is made of the energy taken from the wind during entrainment in the wind. Under conditions such that an excess of energy is available as when the wind is of relatively high velocity or when a slow loss of altitude is desired the maneuvering may take place in a less efficient manner, as by allowing the aeroplane to remain entrained in the wind for an appreciable time before.

detraining, by applying a force other than a centripetal force forcausing the detraining movement, by setting the airfoils to give an ineflicient angle of incidence or by other means.' These and other variations in the method of maneuvering an equipped with a sail area fall within the scope of my invention.

It is to be understood that my invention so far as it relates to the construction of a soaring aeroplane is not limited in its application to monoplanes or biplanes but may be applied well to other types of aeroplanes. The exact number of airfoils which constitute the sail area may be varied to suit different conditions but for practical reasons it is preferable to employ a number of small airfoils rather than one or two large airfoils. So far as I' am aware itisnew to provide an aeroplane with sail areas which can function in the manner described above and therefore I wish it to be understood that the specific mounting of the airfoils which I have described is merely illustrative of my invention. WVithin wide ranges many changes may be madein the airfoil mountings and in the means for maneuvering the airfoils and such aeroplane changes and various other changes in the elements, their relative size, shape and location are contemplated within thescope of my invention.

I claim: o

i l. The method ofsecuringenergy from a wind current for maintaining soaring flight of an aeroplane which consists in absorbing kinetic energy during entrainment of the aeroplane in the wind and utilizing energy thus absorbed to detrain the aeroplane from the wind.

2. The method ofsecuring energy from a wind current for maintaining soaring flight of an aeroplane provided with a sail area which comprises positioning the sail area to absorb inetic energy during entrainment of the aeroplane in the wind and positioning the sailarea to produce a force effective to utilize a portion of the energy thus absorbed to detrain the aeroplane from the wind.

3. The process of maneuvering an aeroplane provided with a sail area in, a wind current which consistsin positioningthe sail area to absorb kinetic energy from the wind during entrainment in the wind and in positioning the sail-area to produce a centripetal force to move the-aeroplane out of entrainment in the wind.

(4.,Tl1e process of maneuvering an aerodplane provided with a sail area in a wind current which consists in positioning'the sail area to produce a forward thrust on the aeroplane during entrainment of the aeroplane ysail area to produce a force in the wind current and i ositioning the Zvliich will transform kinetic energy due to drift velocity into potential energy during-the detraining of the aeroplanlefrom the wind.v 5. In the art of maintaining an aeroplane aloft by soaring flight, the step of detraining the aeroplane from a wind current by presenting an airfoil of the aeroplane to the wind current at such an angle that the lift force therefrom acts upwardly and normal to the drift component of the earth velocity, whereby the kinetic energy due to the drift velocity moves the aeroplane out of entrain ment in-the wind. i

-6. In the art of maintaining an aeroplane, provided with a sail area, aloft by soaring flight in a wind current, the step ofdetraining from the wind current by presenting the 1 sail area to the wind current at such an angle that the lift force produced thereby transforms the kinetic'energ y due to drift velocity into potential energy. i t

, The artlof maintaining an aeroplane, provided with a sail area, aloft by soaring flight in a wind current, which comprises presenting the sail area to the' wind current at such an angle as to produce a lift force having a forward and a drift component, whereby kinetic energy is absorbed from" the wind currentduring entrainment, and presenting the sail area to the wind current at such an angle that the lift force produced thereby acts to turn the drift 'velocity component of the earth velocity upwardly, whereby'the kinetic energy due to drift velocity is transformed into potential energy and the "presenting the sail area to the wind current at such an angle as to produce a lift force havin a forward and a drift component, where y kinetic energy is absorbed from the wind current during entrainment, and presenting the sail area to the wind current at such an angle that the lift force produced thereby acts upwardly and substantially normal to the drift component 'of the earth velocity ofthe aeroplane, whereby the kinetic energy due to drift velocity is transformed into potential energy and the aeroplane is detrained 'from'thc wind current.

i ,9. The method of producing soaring flight of an aeroplane located in a wind current which consists in intermittently absorbing energy'from the wind currentand in utilizing a portion of the energy thus absorbed for supporting said aeroplane during the time when no absorption of energy is taking place."

means for varyingthe angle of incidence of said airfoil. l

.12. An aeroplane comprising supporting wings, an airfoil.mounted on an axis substantially parallel to and fixed with respect to the longitudinal axis of said aeroplane,

means for adjusting the position of said air-' foil with respect to said axis and independent means for-varying the angle of incidence of said airfoil. v

13. An aeroplane comprising supporting wings, aniairfoil support including an axis substantially parallel to the longitudinal axis of the aeroplane and a shaft carried by and normal to said axis, an airfoil carriwl by and having its entering edge parallelto said shaft, and means for altering the position of said airfoil with respect to said axis and, shaft.

14. An aeroplane comprising supporting wings, an airfoil support including an axis substantially parallel to the longitmlinal axis of the aeroplane and a shaft carried by and normal to said axis, an airfoil carried by and having its entering edge parallel tosaid shaft,

means for altering the position of said airfoil With respect to'said axis, and independent means for altering the position of said airfoil with respect to said shaft.

, 15. An aeroplane comprising supporting Wings, a shaft lying substantially parallel to Wings, a rotatably-mounted sail area adapted to absorb energy from the wind and means operable in any position of adJuStment of said sail area for moving'said sail area 1ongi-- tudinally of the aeroplane.

16. A soaring aeroplane comprising supporting wings, a sail area adapted to produce a lift force having a transverse component'directed towards'either "side of the aeroplane, means for varying the angle of attack of said sail area, and independent means for moving the line of application of the lift force pro duced by said sail area longitudinally of the aeroplane. I

17. An aeroplane comprising supporting wings, a shaft lying substantially parallel to a plane which is normal to the longitudinal axis of the aeroplane, an airfoil mounted on said shaft, and means for moving said shaft longitudinally of the aeroplane.

18. An aeroplane comprising supporting a plane which is normal to the ngitudinal axis of the aeroplane, an airfoil mounted on said shaft and having its entering edge parallel to said shaft, and means for moving said shaft longitudinally of the aeroplane.

19. An aeroplane comprising supporting wings, a'sail area effective in a plane substantially normal to said supporting Wings, means for adjusting said sail area to reverse the camber thereof, means operative in any adjustment of said airfoil for varying the angle of incidence thereof, and means for moving said airfoil longitudinally of said aeroplane.

20. A soaring aeroplane comprising supporting wings, a sail area effective in a plane substantially normal to said supporting Wings, means for reversing the camber of said sail area, means for varying the angle of incidence of said sail area and means for moving said sail area longitudinally of the aeroplane.

21. An aeroplane comprising supporting wings, an airfoil which normally lies substantially parallel to said Wings, means for movingsaid airfoil to present the concave face thereof towards either side of the aero-- plane, means for varying the angle of incidence of said airfoil and means for moving said airfoil longitudinally of the aeroplane. In testimony whereof, I affix my signature.

ARTHUR HAL'STED. 

